The present invention relates to a lithium ion battery such as a lithium ion polymer secondary battery having a gel-type or plastic macromolecular electrolyte layer, and a method of manufacturing the same.
In recent years, accompanying by a situation that portable small electric equipment such as small, lightweight cellular phones or portable computers has been popularized, second batteries having small, reliable output characteristics and capable of longtime use by recharging many times such as nickel-cadmium batteries, nickel-hydrogen batteries and lithium ion batteries has been studied and developed vastly as an electric source for supplying electric power to drive the electric equipment.
Among the secondary batteries, the lithium ion secondary battery has characteristics capable of outputting stable electric power despite its small, lightweight, thin in size, and has studied and developed for the purpose of employing as a foldable secondary battery by taking advantage of suitable structural characteristics for its thin size.
Further, as technique capable of achieving the above-mentioned thin size and foldable shape, and of gaining superior characteristics free of leakage unlike the case of employing liquid electrolyte as a div cell, it is suggested that a technique employs gel-type electrolyte including plasticizer realizing flexibility, and a technique employs macromolecular solid electrolyte, in which a lithium salt is dissolved in a macromolecular material.
In such lithium ion secondary batteries with a thin structure, generally, the main part of the battery is formed in the following manner. A laminating structure is formed by laminating a positive electrode, a positive electrode active material layer, a gel-type macromolecular solid electrolyte layer, a separator, a negative electrode, a negative electrode active material layer. A positive electrode lead and a negative lead electrode joints to the corresponding electrodes in the laminating structure. After this, the laminating structure is covered with package members made of aluminum/polypropylene•laminate pack material, and sealed ends.
As for materials used for the above-mentioned schematic structure, for instance, materials described later can be preferably used. Plastic materials employed here are shortened hereinafter: polyethylene terephthalate;PET, fused polypropylene;PP, cast polypropylene;CPP, polyethylene;PE, low-density polyethylene;LDPE, high-density polyethylene;HDPE, linear low-density polyethylene;LLDPE, nyron;Ny. Additionally, aluminum, which is a metal material employed as a barrier film having moisture permeability resistance, is shorten as AL.
The most typical structure is a combination such that a package member, a metal film and a sealant layer are respectively PET, AL, and PE. Other typical laminating structures can be also employed as the same as this combination. Such combinations are: PET/AL/CPP, PET/ALIPET/CPP, PET/Ny/AL/CPP, PET/Ny/AL/Ny/CPP, PET/Ny/AL/Ny/PE, Ny/PE/AL/LLDPE, PET/PE/AL/PET/LDPE, or PET/Ny/AL/LDPE/CPP.
As for materials employed as the sealant layer of a laminating film, the above-exemplified PE, LDPE, HDPE, LLDPE, PP, and CPP and the like can be employed, and its thickness is preferably in a range of 20 μm˜100 μm based on the observed results. The fusion temperature of the materials employed as the sealant layer are generally hereinafter. The fusion temperature of PE, LDPE, HDPE and LLDPE are within a range of 120-150° C., that of PP and CPP are about 180° C., and the fusion temperature of PET employed as the package layer is over 230° C.
As materials employed as a barrier film having moisture permeability resistance, although aluminum is exemplified in the above example, it is not limited, and materials capable of forming thin films by means of sputtering can be employed. As for such materials, alumina (Al2O3), silicon oxide (SiO2), and silicon nitride (SiNx) can be employed.
In a conventional means for sealing the ends of the package members of the lithium ion secondary battery with a thin structure, generally, adhesive material with high adhesion for the metal material and the package members of the lead electrodes, is applied on a position where the ends of the package members are sealed, and pressure is applied on the position to be sealed. In another means, the adhesive material is only applied to surfaces of the sealed positions in each of the lead electrodes and the ends of the package members are applied pressure to each of the lead electrodes so as to seal the part.
However, in the conventional sealing structure and method of manufacturing the same using the adhesive material as described above, there are problems such that even if the package members can be completely sealed to principal surfaces of the lead electrodes, gaps are easy to be produced between sides of the lead electrodes and the package members, which causes an incomplete sealing state (or hermeticity decrease), thereby, insides of the batteries are susceptible to influence of temperature variations or influence from the outside, and by secular change in the batteries, the insides of the batteries deteriorates rapidly, which results in decrease of electromotive force and reduction of durability. Additionally, such batteries occurred the gaps causing degradation of battery capability, must be treated as a nonconforming battery, which results in productivity decrease.